The present invention relates to a variable valve control system for an internal combustion engine, which has two variable valve control mechanisms for varying valve lift characteristics of intake and exhaust valves, and more specifically to a failsafe technique upon malfunction of one of the variable valve control mechanisms. The present invention further relates to a variable valve control method for an internal combustion engine.
For the purpose of improving the output and fuel consumption of an internal combustion engine, there have heretofore been proposed various variable valve control systems for variably controlling the valve lift characteristics of intake and exhaust valves. For example, in a system having valve timing control mechanisms provided to the respective groups of engine cylinders for varying the valve timings of intake and exhaust valves, when a malfunction of one of the valve timing control mechanisms is detected, the valve timing of the other valve timing control mechanism is forcedly controlled so as to coincide with the actual valve timing of the valve timing control mechanism having been detected in malfunctioning, as disclosed in Unexamined Japanese Patent Application No. 5-98916.